Connective Tissue (CT) Proper and Cartilage


Things to Know

  • CT is made of cells + fibers + ground substance

  • ECM = fibers + ground substance

  • Ground substance is a hydrated gel

  • Fibroblasts are the most common CT proper cell and make Type I collagen

  • Collagen = tensile strength

  • Type I collagen is coarse; Type II is fine and often not visible in cartilage; Type III reticular fibers

  • Loose CT generally has more cells/ground substance and thinner collagen bundles

  • Dense CT has thicker/more abundant fibers

  • Cartilage is mostly avascular, so nutrients diffuse through matrix

  • Lacunae are a major clue for cartilage

  • Perichondrium surrounds most cartilage, but there are exceptions

  • Isogenous groups/cell nests = groups of daughter cartilage cells

  • “Blasts” generally = building/growing, “cytes” = maintaining

  • Embryonic CT

    • Mesenchyme → the CT of the developing embryo

What are the two kinds of dense regular CT?

  • Dense Regular → 2 kinds: collagenous and elastic

    • Always regular → the collagen bundles tend to be oriented in the same direction

    • Cells → primarily fibroblasts

  1. Collagenous

    • Most visible → are large bundles of Type I collagen

    • Typical of collagenous ligaments and tendons

  2. Elastic

    • Predominantly large bundles of elastic fibers

    • Reduced amount of Type I collagen fibers

What are the two types of adipose tissue?

  • Adipose tissue

    • Cells → adipocytes

  1. White adipose tissue → white fat

    • Unilocular → each cell has one large lipid vacuole

  2. Brown adipose tissue → brown fat

    • Multilocular → each cell has multiple small lipid vacuoles

Distinguish between loose irregular CT, dense regular & irregular CT, reticular CT, and adipose tissue.

  • Loose irregular CT (areolar CT)

    • Orientation of collagen bundles varies

    • More ground substance and cells than dense irregular CT

      • Highly cellular and fewer fibers

    • Most visible fibers are small/thin bundles of Type I collagen

    • Image ID → lots of open/ground substance + scattered cells + thin collagen fibers

  • Dense irregular CT

    • Orientation of collagen bundles varies

    • Has less ground substance and cells than loose irregular CT

    • Has “wavy collagen”

    • Cells → primarily fibroblasts

    • Most visible fibers are larger/thicker bundles of Type I collagen

    • Image ID → thick, wavy collagen bundles running in different directions

  • Dense regular CT

    • Fibers tend to be oriented in the same direction

    • Cells → primarily fibroblasts

    • Large bundles of Type I collagen or elastic fibers

    • Image ID → fibers are parallel/all running in the same direction

  • Reticular CT

    • Cells → reticular cells

    • Fibers → reticular fibers

    • Form a mesh-like supportive framework

    • Image ID → looks like a mesh/network

  • Adipose Tissue

    • Cells → adipocytes

    • Image ID

      • White adipose → very large clear-looking cells with one large lipid vacuole


      • Brown adipose → cells have multiple small lipid vacuoles

What is the name of the “hydrated gel” polymer that binds to the fibers of the extracellular matrix in cartilage?

  • Hyaluronic acid/hyaluronan

    • Binds multiple aggrecan monomers to form large aggregates

    • Forms a “hydrated gel” with unique compressive properties

List the two cell types of cartilage. Which is actively secreting matrix? (note that visual distinction will not be required, as can be arbitrary)

  1. Chondroblasts

    • Actively secrete cartilage matrix

    • Capable of division and matrix production

    • Produce mostly Type II collagen

    • Blasts = growing

  2. Chondrocytes

    • Not actively dividing and secreting

    • Suspended in cartilage matrix

    • Maintain the matrix

    • Cytes = maintain

Which fiber is visible in fibrocartilage?

  • Type I collagen fibers are visible

Which fiber is visible in elastic cartilage?

  • Elastic fibers are visible

Which fiber is invisible in hyaline cartilage?

  • Type II collagen fibers are invisible

    • It blends into the matrix and cannot be seen

Distinguish between the 3 types of cartilage.

  1. Hyaline cartilage

    • Chondrocytes reside within lacunae

    • Looks “glassy”

    • Type II collagen blends into the matrix and cannot be seen

    • Image ID → glassy/smooth matrix + lacunae + no visible fibers

  2. Elastic cartilage

    • Identical to hyaline except it has elastic fibers

    • Chondrocytes located in frequent isogenous groups

    • Matrix is similar to hyaline cartilage with addition of elastic fibers

    • Image ID → lacunae + visible elastic fibers


  3. Fibrocartilage

    • Small chondrocytes housed within lacunae

    • Chondrocytes inserted between large bundles of collagen fibers

    • Sometimes “stacked” in a row

    • Type I collagen fibers

    • Often arranged in a “herring bone” pattern

    • Image ID → If you see lacunae + fibers = fibrocartilage

      1. This can look like dense irregular CT

      2. But in fibrocartilage, the fiber bundles are “too round: and the cells are located within lacunae


  4. Mixed


    • Hyaline (left) + elastic cartilage (right)

What is the difference between interstitial & appositional growth of cartilage?

  • Interstitial Growth

    • Growth within the inside

    • Chondroblasts divide and form multicellular lacunae → isogenous groups/cell nests

    • Daughter cells secrete matrix around and between each other

    • Causes expansion from within the cartilage

    • Think interstitial = inside

  • Appositional Growth

    • Growth upon the surface (outside)

    • Chondrocytes form from stem cells in the perichondrium

    • Secrete matrix onto the cartilage surface

    • Think appositional = adds onto the outside

Self-Quiz Image ID

  • Brown adipose tissue cells circled in yellow

  • They are multilocular, meaning each cell has multiple small lipid vacuoles

  • Dense CT has much more collagen and much less open ground substance than loose CT

  • There are relatively few cells


  • Loose CT

  • Aka areolar CT

  • Elastic ligaments classified as dense regular CT

  • Fibrocartilage

  • What do we call the CT capsule that surrounds hyaline & elastic cartilage?

    • Perichondrium